The major objective of this work is to isolate, purify and determine the structure of the antitumor alkaloids present in Catharanthus roseus, Catharanthus trichophyllus and Rhazya stricta. The Malagasy plant Catharanthus roseus is a well established source of antitumor agents of the dimeric indole alkaloid class. However several highly active fractions remain to be studied for their active constituents. The crude alkaloid mixtures will be separated initially by pH gradient techniques and subsequently by column chromatography; monitoring each step with an appropriate biological assay. Isolated compounds will be identified by their mp, mass, UV and IR spectra, optical rotation CD and PMR and CMR spectra. Structure elucidation will be carried out by interpretation of these data, chemical correlation with known compounds and in particularly difficult cases by single crystal X-ray crystallography. The alkaloid fraction of the closely related plant Catharanthus trichophyllus also displays very good in vivo antitumor activity and it is proposed to isolate the in vivo active compound from this fraction by techniques similar to those described above for C. roseus. The asian plant Rhazya stricta is at an earlier stage of development. Reports have indicated that extracts of this plant exhibit a marked leucopenic effect and we have confirmed the anticancer activity of the plant. The close botanical relationship of this genus and the genus Catharanthus in the family Apocynaceae makes this a plant for further study.